Iron blue pigment



Patented Sept. 14,1943

IRON BLUE PIGMENT Paul A. Thomasset, St. George, Staten Island,

N. Y.', assignor to Ansbacher-Siegle Corporation, New York, N. Y., acorporation of New York . No Drawing. ApplicationDeeember 17,1941,

Serial No. 423,313

4 Claims. (Cl. 106-304) My present invention relates to the manufactureof colors of the general'type known as iron blues" including Prussianblue. More particularly, it concerns the manufacture of iron blues of atype having a high resistance to alkalies. These colors have a range of"shades varying in accordance with steps practised inthe process ofproduction that are well known in the art and have 'a wide range ofapplication in the printing ink, paint, lacquer, andpigment fieldsgenerally. However, iron blue pigments are very deleteriously affectedby alkalies and as these colors are very' frequently applied to useswhere they come into contact with alkalies,

' they are frequently spoiled. For instance, when.

asoap wrapper is printed with Prussian blue, if sumcient moisture ispresent to dissolve the soap, the wrapper "will be seriously marred andmade unpresentable by reason of the fact thatthe ink will 'be changedfrom arich deep blue,

color to a muddy yellow, and the whole appear ance of the wrapper thusspoiled. v

These colors are generally considered to be a precipitate of ferric,ferrocyanide and formerly were made by precipitating potassiumferrocyanide by ferrous sulphate and thenby oxidizing the bluish whiteprecipitate thus formed tov a 'darker blue, the commercial:Prussian'blue.

More recently, iron blues have been'produced ,by precipitating sodiumferrocyanide with] ferrous sulphate in the, presence of ammoniumsulphate and acid, usually sulphuric acid. The resulting precipitate isthen oxidized by means of various oxidizing agents, such "as sodiumchlorate and sodium bichromate at a temperature-of about 75 C., and theproduct is then filtered,

' washed free oi. soluble salts, and dried in the usual manner. Thepigment so obtained is very satisfactory and in every respect the equalof if not superior to the potassium ferrocyanide product. It has,however, like all iron blues heretfore produced, a vary greatsusceptibility to the action of alkalies, and the color is verydeleteriously affected if it comes into contact therewith.

It is a principal object. of the present invention to provide an ironblue that will have a very high resistance to the action of alkalies,even such strong alkalies as caustic soda.

It may be said broadly that this result is obtained, according to thepresent invention,

by taking such steps in the process of the manufacture of the iron bluesas to reduce the oil absorption very considerably and by adding saltsthe effect of greatly increasing'the resistance of the color to the.action of alkalies.

The first result, namely, that of reducing the oil absorption of thepigment, is in the preferred f processv attained by adding an 8308 5501sodium sulphate. prior to the precipitation, of the whitishprecipitates. It is to be noted here that in the normal reaction of theingredients that throw down this whitish precipitate," sodium sulphateis always formed because of the reaction of the sodium ferrocyanide withferrous sulphate which yields ferrous ferrocyanide and sodium sulphate.However, it is contemplated, according to the process of this invention,to add free sulphate to a solution of ferrous sulphate,-ammoniumsulphate, and sulphuric acid, all these ingredients being dissolved inwater at a temperature'of about 30 C, This addition of sodium sulphateis a departure from the usual formula of manufacture which normallyresults in the undesired and unavoidable production of a large amount ofsodium sulphate due to the above described reaction which takes placeupon the addition of ferrocyanide in an aqueous solution at 30 C. I

Upon 'the addition ofthe sodium ferrocyanide, The precipitate issulphate or cobalt chloride, are added. The product resulting has a'very high degree of resistance to the action of alkalies.

In mycopending application Serial No. 304,547, now Patent No.-2,275,929, granted March 10, 1942, of which the present application is acontinuation-impart, I have disclosed a formula for carrying out theinvention which calls for the addition of water-soluble nickel or cobaltsalts, or mixtures of the two, to be added to accomplish the purpose 'ofthe invention. The present ap'-- plication, however, is limited to theuse of the said mixtures ofwater-soluble nickel and cobalt salts.

A formula according to the present invention follows;

First, a solution in water at about 30 C. is made of k. of ferroussulphate, 21.4 k. of ammonium sulphate, 15 k. of sodium sulphate, and2.1 k. of 66 Baum sulphuric acid in 500 liters of water. To this isadded a solution of 100 k. of sodium ferrocyanide dissolved'in 1000liters of water at 30 C. which is added slowly with stirring. Uponprecipitation, the temperature is increased to C. and 3.5 .k. of a mixofcertain metals of the iron group which have as ture of nickel sulphateand cobalt chloride dis- -v solved in 50 liters of water is added. Thewhole is .stirred for a few minutes and an additional portion of 24.4 k.of sulphuric acid .66 Baum is then added- Oxidation is then carried outby the rate in 50 liters of hot water. The batch is then stirred for a,few minutes, filtered, washed free of soluble salts, and dried in theusual manner.

such as nickel ammonium sulphate and nickel chloride, and other watersoluble nickel and cobalt salts which also give substantially the samehigh resistancetoalkalies.

.It.isto beunderstoodthatcertain nickel and cobalt salts, such as nickelhydroxide or cobalt hydroxide, which are insoluble salts hythemselves,'become soluble in the presence of sul-' phuric acid and mayaccordingly be usedwith the same eflect as the nickel and cobalt saltsabovementioned.

Sodium sulphate is, of course, a soluble salt and, regardless of whetherit is produced by the reaction of the ferrous sulphate and sodiumferrocyanide or whether it isadded in the free state, it iseliminatedduring the washing and drying step and does not appear in. theultimate product. 7

The process of this invention is, of course, not limited to iron bluesproduced by the sodium ferrocyanide process described above as apreferred process, but is applicable to the potassium ferrocyanideprocess referred to hereinabove and to other alkali ferrocyanideprocesses ofasaaacs making iron blues-as well. But in any case, theprocess would be advantageously exemplifled in that it calls for thereduction of oil abjsorption and the addition of saltsof the iron groupmetals are'hereinbefore described.

' Having thus described my invention, what I claimis: 1. A process formaking alkali resisting iron blues which comprises dissolving in waterat 10 about 30 C. ferrous sulphate, ammonium s'ulphate and sulphuricacid; adding thereto free sodium sulphate in aqueous solution; thenre--.

acting said solution with asolution of sodium ferrocyanide in water,thus forming a whitev pre- 5 cipitate; raising the temperature of thefprecipitate to about 75 C. and adding an aqueous solution of nickelsulphate .and cobalt chloride to said precipitate and oxidizing the massto a blue 1 color bythe addition of sulphuric acid and an aqueoussolution of sodium chlorate. i

2. An alkali resisting iron blue comprising the oxidized reactionproducts of ferrous ferrocyanide, an aqueous solution of nickel andcobalt salts and sulphuric acid. I v 3. An alkali resisting iron bluecomprising the reaction products resulting from the addition of anaqueous solution of salts of nickel and cobalt to azprecipitate formedby the .reaction of an" aqueous solution of sodium ferrocyanide' sowithasolution of ferrous sulphate, ammonium sulphate and sulphuric acid; saidreaction products being oxidized to a blue color. v

' 4. An alkali resisting iron blue comprising the oxidized reactionproducts resulting from the addition of salts of .nickel and cobaltthatbecome water soluble in the presence of sulphuric acid, to aprecipitateformed by the addition of sodium ferrocyanideto an aqueoussolution of ferrous sulphate, ammonium sulphate, sodium sulphateandsulphuric acid.

PAULA. momssn'r.

